This invention relates to a direct injection fuel injector for an internal combustion engine.
Combustion chamber deposits have been a cause of concern in gasoline internal combustion because such deposits are believed to affect, to name a few, driveability, emission, ignition plug fouling and degraded injector performance. In the case of a direct injection gasoline engine, deposits may be formed on the surfaces of the combustion chamber, valves, piston, injector and spark plugs. In particular, it is believed that these surfaces are often wetted with fuel, thereby increasing the likelihood of deposit formations. The formation of deposits on the surfaces of the injector is believed to cause flow capacity shift and spray pattern degradation that result in power loss, engine roughness and increased emissions for the direct injection gasoline engine. Moreover, it is believed that the direct injection fuel injector is especially affected since the injection pressure is oftentimes too low to mechanically dissociate the deposits that are formed on the wetted surfaces of the injector, such as the seat and needle or closure member.
Research on combustion deposits formations appears to indicate that the formation of deposits on the injector tip is dependent on a variety of factors including an injector tip temperature, injector protrusion into the combustion chamber, heat transfer from the injector to the coolant passages of the engine, types of fuel, surface geometry of the injector tip and coating or plating of the tip surfaces. The data also seems to indicate that where the injector tip temperature is above 110-140 degrees Celsius, a tendency for a formation of deposits is increased when the other factors are unchanged. Conversely, the data seems to indicate that below this temperature (approximately 120xc2x0 Celsius), the tendency for the formation of injector tip deposits is greatly reduced when the other factors are held constant.
The present invention provides for a method of selecting at least one optimal combination of engine or fuel injector characteristics that minimizes injector tip deposit formation of one or more selected internal combustion engine and fuel injector from a plurality of direct injection engines and direct fuel injectors, each of the engines and fuel injectors having characteristics selected from a plurality of engine and fuel injector characteristics. Preferably, the method is achieved by: (a) generating at least one map that relates engine load, engine speed and injector tip temperature for an operating range of the engine, the combination operating at a generally stochiometric air-fuel mixture; (b) determining changes in fuel flow through the injector when the combination is operated at one or more selected points of the at least one map over a selected period of time; (c) generating at least one engine-characteristic map as a function of: (i) changes in fuel flow obtained while performing (b); (ii) injector tip temperature obtained while performing (a); (d) performing (a)-(c) for at least another combination; and (e) selecting one combination that has the least amount of changes in fuel flow being indicated on the at least one engine-characteristic map generated in (c).
The present invention further provides for a method of selecting optimal engine and fuel injector characteristic that minimizes injector tip deposit of a particular fuel injector operating with a particular engine. In one preferred embodiment, the method is achieved by (a) generating at least one map that relates engine load, engine speed and injector tip temperature for an operating range of the engine, the combination operating at a generally stochiometric air-fuel mixture; (b) evaluating the at least one map to determine whether the at least one combination includes a tendency to form injector tip combustion deposits; and (c) generating at least one engine characteristic map when the evaluating indicates a tendency of the combination to form combustion deposits on the injector, the engine characteristic map being generated as a function of changes in fuel flow by determining changes in fuel flow through the injector when the combination is operated at one or more selected points of the at least one map over a selected period of time, and injector tip temperatures obtained from (a).